Solar-powered plants promise water for world’s poorest

By Ernest Gill Hamburg (Germany), March 4 (DPA) A team of German scientists has come up with a revolutionary design for a small solar-powered mobile water treatment plant which could bring hope to drought-affected areas of the world. The researchers from the Fraunhofer Institute for Solar Energy Systems (ISE) in Freiburg said they have been carrying out tests on their small, decentralised water treatment plants with an autonomous power supply in recent weeks and that they hope they will move into production in the coming months.

According to the team, the plant can produce 120 to 150 litres of pure drinking water per day from salty seawater or brackish water.

“Our plants work on the principle of membrane distillation,” explained one of the team, Joachim Koschikowski.

“In our plant, the salty water is heated up and guided along a micro-porous, water-repellent membrane. Cold drinking water flows along the other side of the membrane.

“The salt is left behind and the water vapour condenses as it cools on the other side. It leaves us with clean, germ-free water.”

The team said that the units could be particularly useful for communities in rural parts of Africa and India, where there are no funds for permanent desalination plants.

Tests in Gran Canaria and Jordan of the new system have already proved very successful.

The plant on Gran Canaria has been up and running for three years, Koschikowski said. So far, only little things have needed repair, such as the odd cable or the pump that had to be replaced.

“But those are teething problems,” he said. “In principle, the plant has been designed to be maintenance free.”

The desalination system is based on the principle of membrane distillation.

“The salty water is heated up and guided along a microporous, water repellent membrane,” Koschikowski explained.

“Cold drinking water flows through the other side of the membrane. The steam pressure gradient resulting from the temperature difference causes part of the salt water to evaporate and pass through the membrane. The salt is left behind, and the water vapour condenses as it cools down on the other side. It leaves us with clean, germ-free water.”

In comparison, other methods such as reverse osmosis or solar water distillation are either too sensitive to impurities in the water or too inefficient.

Membrane distillation plants, on the other hand, are rather robust and uncomplicated. In addition, the system recovers the heat after the distillation process, making it more energy-efficient.

The Fraunhofer researchers have also developed a dual-circuit system in which several desalination modules are connected, so that the system is more powerful and reaches a greater output of several cubic metres of water treated per day.

Even though, compared to this, up to 150 litres of drinking water from the compact plants might seem like a drop in the ocean, Koschikowski said that there is definitely a demand for the small capacity, too.

In developing countries, water consumption is much lower than in developed countries. Hence, a small plant can supply drinking water for up to 15 people.

The price per 1,000 litres will amount to about 10 euros ($15) as soon as the plants can be mass-produced.

“When you think how much the inhabitants currently have to pay for the same amount of bottled water or soft drinks, the plant will pay off very quickly,” Koschikowski concluded.